Hi Sanjaya Kodagoda,
As for your first question the default behavior of the control is that it will select/deselect the item by clicking on both node and checkbox. The only situation is if trying to select the already selected item then it will deselect the item. This is the default behavior of the control.
For your next question Unfortunately I couldn't replicate any issue. Please have a look into this online demo
and try to replicate it here.